/Engine/Plugins/Online/OnlineSubsystem/Source/Public/Interfaces/OnlineSessionInterface.h
Delegate fired when the un-registration process has completed
typedef TMulticastDelegate_ThreeParams< void, [FName](API\Runtime\Core\UObject\FName), const [TArray](API\Runtime\Core\Containers\TArray)< FUniqueNetIdRef > &, bool > FOnUnregisterPlayersComplete